The present invention relates to a drive apparatus of working machine such as an excavator, a crane and the like that uses an engine such as a diesel engine and the like as a power source, and in particular to a drive apparatus of working machine, in which an electric motor concurrently serving as a generator and a battery, which are connected to one end of an output of engine, supplement the output of the engine.
Conventionally, a working machine such as an excavator, a crane and the like is generally provided with an engine such as a diesel engine and the like in order to obtain a power for self-traveling, by which a hydraulic pump is driven, and the rotation of crawlers or tires for traveling and the movement of each working part such as a boom, an arm, a bucket and the like are performed by supplying hydraulic oil discharged from the hydraulic pump to a hydraulic actuator such as a hydraulic pump, a hydraulic cylinder and the like.
FIG. 13 is a view showing a general construction of a self-traveled excavator, FIG. 14 is a graph showing a relationship between discharge flow rate and discharge pressure of a hydraulic pump, and FIG. 15 a graph showing a relationship between the number of revolutions and output torque of an engine.
In FIG. 18, the self-traveled excavator comprises traveling crawlers 102 having left and right travel-driving hydraulic motors 101, and an upper rotating body 103 is provided on the traveling crawlers 102 to be rotatable about a vertical axis. The upper rotating body 103 is provided with an engine 105, a hydraulic pump 106, a hydraulic oil tank 107, a fuel tank 108, a rotation-driving hydraulic motor 109, a rotation-driving decelerator 110 and the like as well as a cab 104. In the front part of the upper rotating body 103, a boom 111, an arm 112, and a bucket 113 are provided as working members for performing the working, which are connected to be actuated by a boom cylinder 114, an arm cylinder 115, and a bucket cylinder 116, respectively. The hydraulic pump 106 is rotated by using the output of the engine 105 as a power source and the travel-driving hydraulic motor 101, the rotation driving hydraulic motor 109, the boom cylinder 114, the arm cylinder 115, and the bucket cylinder 116, which actuate respective working members, are driven by using hydraulic oil discharged from the hydraulic pump 106.
For the hydraulic pump 106, e.g. a variable discharge pump may be used, and its output is controlled to have a constant power (discharge pressure x discharge flow rate) characteristic in relation to discharge pressure and discharge flow rate, thereby to be set to a value near a rated output of engine so that its output shall not exceed the nominal power of engine. By this, it is envisaged that the power of engine can be utilized at its most while preventing the absorbed horse power of the hydraulic pump from exceeding the nominal power of engine to cause an engine stall (ENST).
As shown in FIG. 14, the constant power characteristic of a variable discharge pump is indicated as a hyperbola on the plane of discharge pressure-discharge flow rate, and the input of pump (B) is set to a value near the rated output (A) of the engine, so that the rated output of the engine can be utilized as much as possible.
In addition, as shown in FIG. 15, the engine 105 has a torque rising characteristic in the range below the rated number of revolutions, while it has a characteristic that both of its output and torque are reduced, in the range from the rated number of revolutions to the number of high idle revolutions.
In order to efficiently use the power of engine, the engine 105 reaches to the maximum (rated) number of revolutions when the input of hydraulic pump 106 is at the maximum, and is operated near the rated number of revolutions. Therefore, if the input of hydraulic pump becomes smaller, the number of revolutions of engine shifts toward the number of high idle revolutions and is operated in the number of revolutions higher than the rated number of revolutions. The number of high idle revolutions is higher than the rated number of revolutions up to about 10%.
Further, in a transition state where the input of hydraulic pump 106 is temporarily increased larger than the output of the engine 105, the number of revolutions of engine is decreased lower than the rated number of revolutions due to a delay in control of the variable discharge pump and the like, whereas the output torque of the engine is increased and the engine stall is prohibited due to the torque rising characteristic of engine. In this way, engine is operated between the rated number of revolutions and the number of high idle revolutions in the normal state except the transition state.
Like this, the reason why the power by hydraulic pressure is used as a drive apparatus is that it has some merits as compared to electric power in that (1) because driving machinery and tools are light and compact, they are suitable to be mounted in a working machine to meet its self-traveling movement, and (2) it is easy to obtain a large reciprocating thrust if a hydraulic cylinder is used. However, power by hydraulic pressure has a problem in that energy efficiency for working is poor as compared to electric power. In a hydraulic circuit, by performing the control of directions, pressure and flow rate for hydraulic fluid discharged from the hydraulic pump using a control valve, actuating direction, actuating force and actuating velocity of a hydraulic actuator are controlled. In this case, if the proportion of hydraulic energy bled and wasted by the control valve for performing the control of pressure and flow rate of hydraulic oil is large, and when the energy supplied from the power source is used for working, the loss of energy is large.
Furthermore, the energy needed by a working machine to perform a work is varied with the lapse of time in accordance with the content of work to be formed; there were problems in that an engine which is a power source should have a capacity that can provide a maximum input energy required by a hydraulic pump, and the utilization efficiency of engine power is low.
Therefore in recent years, in order to overcome the lowering of utilization efficiency of the engine power and the deterioration of utilization efficiency of hydraulic power, the following techniques have been proposed, from the view of saving energy.
Firstly, an internal combustion engine for a hydraulic excavator has been proposed, wherein an inductor is provided in a power line of engine and the combustion engine comprises a battery for accumulating electric energy regenerated by the inductor, an inverter circuit for converting electric energy accumulated in the battery into AC electric power and supplying it to said inductor as well as for converting AC electric power regenerated by the inductor into DC electric power and supplying it to said battery, and a switching means for switching and controlling the actions of said inverter circuit (Japanese Utility Model Unexamined Publication No. Hei 5-48501:first prior art).
This is to operate the inductor as a regenerative generator to charge the battery with electricity via the inverter circuit when the work performed by the working machine is a low load one in which the engine power has a margin, and to operate the inductor as an electric motor using the electric power accumulated in the battery via the inverter circuit to assist the engine when the work performed by the working machine is a high load work in which a power larger than the engine power is required.
By this, it becomes possible to cope with all kinds of works using an engine, the capacity of which is smaller than a maximum working energy required by the hydraulic pump (rated power of engine in FIG. 14(C)), whereby it is envisaged that the engine can be miniaturized to efficiently utilize the power of engine.
Next, it has been also proposed to provide a rotating hydraulic pump motor that performs rotation driving of a rotation system, an accumulator for driving said rotating hydraulic pump motor and a rotation controller for switching and controlling the action of said rotating hydraulic pump motor, wherein said rotating hydraulic pump motor is operated in a pump action to regenerate rotational energy at the time of braking the rotation system, and additionally an electric motor concurrently serving as a generator is installed in the rotation pump motor, so that the power generating action and assisting action of said electric motor will be switched by controlling the switching of a rotation controller (Japanese Patent Unexamined Publication Hei 10-103112:second prior art).
According to this, it is envisaged that energy can be saved by accumulating rotational energy at the time of braking the rotation system and reusing it at the time of rotation, and the deterioration of energy efficiency in the hydraulic circuit can be improved.
There were problems in the prior art using the engine installed with the inductor, which is the first prior art, in that because the inductor is switched between the power generating action and driving action in accordance with variation of work load, the work load may be larger than the engine output so that when the inductor is switched to the driving action, the number of revolutions of engine may be largely reduced, for example, from 2000 rpm to 1400 rpm, which appears as the variation of velocity in driving the hydraulic circuit, whereby the utilization convenience thereof in manipulating the working machine will be deteriorated.
And, in the case of the drive apparatus used in rotation driving the rotating hydraulic pump motor, which is the second prior art, there was also a problem in that regenerated hydraulic energy can be used only in rotation driving the rotation system.
Furthermore, according to the prior art as explained in the above, because the actuator, which is a driving part, is driven by a hydraulic pump directly coupled to an engine and/or a pressure accumulating means, it is possible to realize smooth action following the movements of manipulation lever when moving the arm or the boom of the hydraulic excavator, whereas there was a problem that energy efficiency becomes deteriorated because the hydraulic pump directly coupled to the engine the like is used in driving an actuator, and according to said prior art, it was impossible to meet with both of the maneuverability of drive apparatus of working machine and relatively high energy efficiency.
In view of the problems of the prior art, the primary object of the present invention is to provide a drive apparatus of working machine, which is improved in utilization convenience while attaining the improvement in utilization efficiency of energy.
Also, the secondary object of the invention is to provide a drive apparatus of working machine having a relatively high efficiency of energy while attaining a good maneuverability of moving parts.
According to the first aspect of the present invention, the drive apparatus of working machine comprises: an engine; a hydraulic pump connected to said engine and having a maximum input larger than an output of said engine; an electric motor concurrently serving as a generator which is connected to the output shaft of said engine and performs a generator action or an electric motor action; a battery for accumulating electric power generated by said electric motor concurrently serving as a generator; a first control device connected to said electric motor and said battery to switch the actions of said electric motor, the first control device charging said battery with electric power generated by rotation of said electric motor at the time of the generator action, and supplying electric power accumulated in said battery to said electric motor to rotate it at the time of the electric motor action; and a controller connected to said first control device, wherein when an input of said hydraulic pump is smaller than said output of the engine, said controller operates said engine between the set number of revolutions and, the number of high idle revolutions of the engine and when the input of said hydraulic pump is larger than the output of said engine, said controller reduces the input of the said pump and operates said electric in the electric motor action using the electric power accumulated in said battery to supplement that the output of said engine will, so that said engine will be operated near the set number of revolutions.
According to this construction, because the number revolutions of the engine is stable and the engine is operated in the set number of revolutions even if the input of hydraulic pump is larger than the output of engine, it is not affected by the variation of velocity in the hydraulic circuit and the utilization convenience of working machine will not be deteriorated. In other words, the drive apparatus of this working machine comprises the first control device that charges the battery with electricity by the electric motor connected to the engine at the time of low load working and drives the electric motor concurrently serving as a generator using the electric power accumulated in the battery to assist the output of engine at the time of high load working, and the controller that controls the number of revolutions of the engine to be turned to the set number of revolutions when the electric motor concurrently serving as a generator is operated in the generator action, whereby it is possible to use an engine, the output of which has a capacity smaller than the maximum input of hydraulic pump, and the utilization convenience of the working machine will not be deteriorated because the number of the engine is stably maintained.
Also, according to the second aspect of the present invention, the drive apparatus of working machine comprises: an engine; a hydraulic pump connected to said engine and having a maximum input larger than the output of said engine; an electric motor concurrently serving as a generator which is connected to an output shaft of said engine and performs a generator action or an electric motor action; a battery for accumulating electric power generated by said electric motor concurrently serving as a generator; a second control device connected to said electric motor and said battery to switch the actions of said electric motor the second control device charging said battery with electric power generated by rotation of said electric motor at the time of the generator action, and supplying electric power accumulated in said battery to said electric to rotate it, at the time of electric motor action; a generator concurrently serving as a rotating electric motor that rotates a rotating body of the working machine and performs an electric motor action or a generator action; and a third control device connected to said generator currently serving as a rotating electric motor and said battery to switch the actions of said generator concurrently serving as a rotating electric motor, the third control device operating said generator concurrently serving as a rotating electric motor in the electric motor action to drive said generator concurrently serving as a rotating electric motor using the electric power accumulated in said battery, at the time of rotating the rotating body, and operating said generator concurrently serving as a rotating electric motor in the generator action to charge said battery with the electric power generated by said generator concurrently serving as a rotating electric motor, at the time of braking the rotating body.
According to this construction, because the battery can be charged with electricity by operating the generator concurrently serving as a rotating electric motor in the generator action to perform regenerative braking the revolution, it is envisaged that energy can be reused without bring a rise in temperature of hydraulic oil and can also be reused other than rotation driving. In other words, the drive apparatus of this working machine comprises: the second control device that charges the battery with electricity by the electric motor concurrently serving as a generator connected to the engine, at the time of low load working, and drives the electric motor concurrently serving as a generator using the electric power accumulated in the battery to assist the output of engine at the time of high load working; the generator concurrently serving as a rotating electric motor for rotating the rotating body; and the third control device that charges the battery with electricity by said generator concurrently serving as a rotating electric motor, at the time of braking rotation and drives the generator concurrently serving as an electric motor using the electric power accumulated in the battery, at the time of rotation, whereby energy can also be reused for driving other than the rotating system and energy can be saved.
Furthermore, according to the third aspect of the present invention, the drive apparatus of working machine of the second aspect of the present invention as explained in the above, further comprises a controller connected to said second control device and said third control device, wherein when an input of said hydraulic pump is smaller than the output of said engine, said controller operates said engine between the set number of revolutions and the number of high idle revolutions, and when the input of said hydraulic pump is larger than the output of said engine, the controller reduces the input of said hydraulic pump and operates said electric motor concurrently serving as a generator in the electric motor action using the electric power accumulated in said battery to supplement the output of said engine, thereby operating said engine near the set number of revolutions.
According to this construction, because the number of revolutions of the engine is stable and operated in the set number of revolutions when the input of the hydraulic pump is larger than the output of the engine, the utilization convenience will not be deteriorated without being affected by the variation of velocity in the hydraulic circuit, and because the battery can be charged with electricity by operating the generator concurrently serving as a rotating electric motor in the generator action to perform regenerative breaking, at the time of breaking of the rotation body, the energy can be reused besides rotation driving.
Also, according to the fourth aspect of the present invention, in the drive apparatus of working machine according to any of the first to third aspects of the present invention, said engine and said electric motor serving as a generator are connected via an accelerating apparatus.
According to this construction, because the electric motor can be operated in a higher number of revolutions, it is possible to make the electric motor concurrently serving as a generator in a compact form and the space for locating it can be reduced.
In addition, the drive apparatus according to the fifth aspect of the present invention comprises: an engine; a first hydraulic pump driven by said engine; a first hydraulic actuator connected to said first hydraulic pump via a control valve; an electricity storage means for accumulating electric energy, an energy conversion means which can selectively perform a function that converts mechanical energy received from said engine into electric energy to supply to said electricity storage means and a function that converts electric energy received from said electricity storage means into mechanical energy to supply to said first hydraulic pump; and a first electric motor that receives a supply of electric energy from at least one of said energy conversion means and said electricity storage means and serves as a driving source of moving parts.
According to this construction, because the first hydraulic pump driven by the engine is connected to the first hydraulic actuator via the control valve, it is possible to attain a good maneuverability for moving parts, for example, an arm, a boom, and the like of excavator, which need to be smoothly moved following the movements of a manipulation lever.
Also, because the first electric motor that receives electric energy from at least one of the energy conversion means and the electricity storage means serves as a driving source for moving parts, it is possible to increase the energy efficiency, as compared to the prior art by using the first electric motor as the driving source of moving parts which do not require high maneuverability, for example a bucket of hydraulic excavator, a rotating system, a traveling system and the like.
That is, in the drive apparatus of working machine of this construction, the moving parts, which require good maneuverability are driven by the first hydraulic pump and the first electric motor is made to be serve as a driving source for the moving parts which do not require good maneuverability, whereby it is possible to realize relatively high efficiency of energy while attaining good maneuverability of the moving parts.
Also, because the moving parts are separated into two groups, the one operated by the first hydraulic pump and the other operated by the first electric motor, they can be made in a relatively small size, respectively, and separately mounted in different places. For example, the first hydraulic pump may be located within the main shell of the first hydraulic pump and the first electric motor may be located adjacent corresponding moving parts, whereby it is possible to provide a compact drive apparatus without requiring to provide a large space in one place.
Furthermore, because the energy conversion means can selectively perform the function that converts mechanical energy received from the engine into electric energy and supplies it to the electricity storage means, and the function that converts electric energy received from the electricity storage means into mechanical energy and supplies it to the first hydraulic pump, a surplus torque of engine can be used to perform generation of electric power for a accumulating electric energy in the electricity storage means, at the time when the first hydraulic pump side is low loaded, and the electric energy accumulated in the electricity storage means can be used as a driving source and the energy conversion means can be used as a motor to supplement the torque of the first hydraulic pump, at the time when the first hydraulic pump side is high loaded, whereby it is possible to equalize and reduce the burden of engine. For this reason, the engine may have a dimension that can take a share of average output and need not to be made so large to cope with the maximum output, whereby it is possible to reduce the engine size, to decrease exhaust gas and noise, and to save energy.
Still, according to the sixth aspect of the present invention, in the drive apparatus of working machine of the fifth aspect, the electric energy generated by regenerative control of said first electric motor is accumulated in said electricity storage means.
According to this construction, because the electric energy generated by regenerative control of said first electric motor is accumulated in the electricity storage means, it is possible to increase the energy efficiency much higher.
Yet, according to the seventh aspect of the present invention, the drive apparatus of working machine of the fifth aspect further comprises a second hydraulic pump driven by said first electric motor, and a second hydraulic actuator driven by said second hydraulic pump.
According to this construction, because the second hydraulic pump driven by said first electric motor drives the second hydraulic actuator, a large thrust can be supplied when it is required to perform a linear movement of a moving part, and the construction is simple as compared to the case that a rack and pinion mechanism and the like convert linear movements into rotating movements.
Still yet, according to the eighth aspect of the present invention, in the drive apparatus of working apparatus of the seventh aspect, said first electric motor, said second hydraulic pump and said second hydraulic actuator are integrated as one unit.
According to this construction, because the first electric motor, the second hydraulic pump and the second actuator are integrated, they can be miniaturized and low-weighted, and when the second hydraulic actuator is not required to be operated, it is possible not to waste surplus hydraulic oil by stopping the corresponding first electric motor and second hydraulic pump. Accordingly, the energy efficiency can be more increased. In addition, because it is not required to provide a piping for coupling the second hydraulic pump and the second actuator, the construction can be simplified and the likelihood of leakage can be decreased.
Furthermore, according to the ninth aspect of the present invention, the drive apparatus of working machine of the fifth aspect further comprises a second electric motor that receives electric energy from at least one of said energy conversion means and said electricity storage means, and a third hydraulic pump driven by said second electric motor, pressure oil from said third hydraulic pump being supplied between said first hydraulic pump and said control valve.
According to this construction, because the pressure oil from said third hydraulic pump is supplied between said first hydraulic pump and said control valve and hence the pressure of the oil in this portion can be fixedly maintained, the operation starting position of the manipulation lever will not be changed by the load applied to the first hydraulic actuator and the first actuator always starts to move from a fixed position of the manipulation lever, thereby improving the maneuverability. In addition, it becomes possible to fixedly maintain the operation starting position of the manipulation lever even by merely compensating the variation of load applied to the first hydraulic actuator with torque assist by the energy conversion means.